The demand for more effective filtration of air in sealed disk drive devices continues to increase as the disk drive industry moves toward higher performance, higher capacity and smaller sealed drives. Drive cleanliness and heat dissipation are extremely important if not critical factors. With respect to the cleanliness factor, sealed disk drive systems presently use a breather/pressure equalizing filter and a recirculating filter. Generally, the breather filter is a flat sheet, high efficiency media filter, while the recirculating filter is a lower efficiency, pleated unit. The present invention is directed to a flat sheet media filter device for particularly the recirculating filter, and also to a combination of flat sheet media for both filters in the same housing.
A typical sealed disk drive system is shown in FIGS. 1 and 2 of the drawings. Housing 20 contains platters 21 on spindle 22. Actuator arms 23 move read/write heads 24 as required. Since the distance between the platters and the read/write heads is crucial, the presence of small contaminating particles can affect the system. As the platters spin, centrifugal force causes a circulation of air in housing 20. A filter 25 is located to receive the moving air and clean it. In addition, a breather filter 27 cleans make-up air. During operation, regions of low pressure are created, particularly in the area of the spindle, and make up air is needed to equalize pressure relative to ambient. Also, the bearing 26 which journals spindle 22 is often sensitive to pressure differentials, and, care must be taken to maintain as near an equal pressure to ambient within housing 20 as possible. In addition, as temperature rises in housing 20 after a period of continuous operation, pressure also rises and it may be necessary to release air from within housing 24. For these reasons, breather filter 27 is commonly installed in a wall of housing 20. Although breather filter 27 is known to be made from flat sheet filter media, recirculating filter 25 is commonly a pleated unit. In the interest of reducing space as units become smaller, the present invention is directed to an air filter device of a flat sheet media type for replacing the pleated recirculating filter of the art.
Two known techniques for assembling flat sheet filter media by means of ultrasonic welding are shown in FIGS. 3 and 4. In FIG. 3, the filter media 28 is ultrasonically welded at ring 29 to plastic frame 30. A concern is that fraying at the cut edge of the filter media over time is subject to releasing particles and strands of material into the housing environment. The technique of FIG. 3 uses an adhesive ring 31 to contain cut edge 32 of media 28 between weld ring 29 and frame 30.
In FIG. 4, filter media 33 is mechanically pinched between structures 35 and 36 of frame halves 37 and 38 to contain the cut edge of media 33 between the pinching structures and ring 39. Frame halves 37 and 38 are ultrasonically welded together at ring 39.
The problem addressed by the present invention then is to provide a housing for flat sheet filter media which receives recirculating air from within a sealed housing and directs that air through the flat sheet filter media. Sufficient media area must be available to allow a sufficient volume of air to pass through the media without developing an unnecessary resistance to the flow of air. Also, the cut edge of the filter media must be encapsulated.